Determination of Nitrogen/Protein in Milk and Milk Products (FP928)

Význam tématu

Protein determination in milk and dairy products is critical for nutritional labeling, quality assurance and economic valuation. Rapid, accurate methods support process control, regulatory compliance and product specification.

Cíle a přehled studie / článku

The application note describes the use of the LECO FP928 macro combustion Nitrogen/Protein determinator for measuring total nitrogen and calculating protein content in milk, half-and-half, buttermilk and plant-based milk. The study aims to demonstrate method performance, calibration, precision and the effects of carrier gas and aliquot loop size.

Použitá metodika a instrumentace

The FP928 employs high-temperature (1100 °C) combustion in pure oxygen, converting sample nitrogen to NOx, which is reduced to N₂ over copper and detected by thermal conductivity. Carrier gases can be helium (highest sensitivity) or argon. Two aliquot loops (3 cm³ and 10 cm³) allow optimization for low or high nitrogen ranges.

• Sample mass: ~1.000 g loaded into ceramic combustion boats with nickel liners
• Calibration: linear, forced through origin with glycine solutions (1.0 % N) and verified at 0.5 % N glycine and 0.1 % N ammonium standards
• Instrument parameters: furnace 1100 °C, purge cycles 3, ballast equilibration 10 s, aliquot loop size selectable, integration times 50–70 s depending on carrier gas

Hlavní výsledky a diskuse

Analysis of four matrices showed:

• Whole milk: average 0.505 % N (3.225 % protein)
• Half-and-half: average 0.452 % N (2.882 % protein)
• Buttermilk: average 0.547 % N (3.490 % protein)
• Oat milk: average 0.129 % N (0.824 % protein)

Helium provided improved precision (standard deviation ≤0.001 % N) versus argon (≤0.005 % N). Loop size had minimal effect on average results but influenced reagent life and cost per analysis.

Přínosy a praktické využití metody

The Dumas combustion approach offers rapid throughput (<5 min per sample), high precision, minimal chemical waste and full automation. It is well suited for routine QA/QC laboratories, dairy processing plants and research settings.

Budoucí trendy a možnosti využití

Advances may include further miniaturization of combustion chambers, integration with robotics and LIMS, real-time data analytics, expanded applications to non-dairy matrices and coupling with isotope ratio mass spectrometry for detailed profiling.

Závěr

The LECO FP928 Dumas method delivers reliable, high-precision nitrogen and protein determinations in diverse milk products. The flexibility of carrier gas selection and aliquot loop sizes ensures broad applicability for routine and specialized analyses.

Reference

• ISO 14891:2019, Milk and Milk Products – Determination of Nitrogen content – Routine method using combustion according to the Dumas principle
• USDA Circular No. 183, Protein Factor for Various Materials
• LECO FP928 Series Operator’s Instruction Manual, LECO Corporation